The COMMODORE PET (PERSONAL ELECTRONIC TRANSACTOR) is a line of home
/personal computers produced starting in 1977 by Commodore
International . A top-seller in the Canadian and United States
educational markets, it was Commodore's first full-featured computer,
and formed the basis for their entire
8-bit product line, including
the
Commodore 64 . The first model, which was named the PET 2001, was
the third personal computer ever made available to retail consumers,
after the
Apple II and
TRS-80 .

* 2.1 PET 2001 series / 2001-N "> The chiclet keyboard of the PET
2001 series The integrated Datasette reader PET 2001
with its top lifted

In the 1970s Commodore was one of many electronics companies selling
calculators designed around
Dallas -based
Texas Instruments (TI)
chips. However, in 1975 TI increased the price of these components to
the point where the chip set cost more than an entire TI calculator,
and the industry that had built up around it was frozen out of the
market.

Commodore responded to this by searching for a chip set they could
purchase outright. They quickly found
MOS Technology , which was in
the process of bringing its 6502 microprocessor design to market, and
with which came
Chuck Peddle 's
KIM-1 design, a small computer kit
based on the 6502. At Commodore, Peddle convinced
Jack Tramiel that
calculators were a dead-end. In September 1976 Peddle got a
demonstration of Jobs and Wozniak 's
Apple II prototype, when Jobs was
offering to sell it to Commodore, but Commodore considered Jobs' offer
too expensive. Tramiel demanded that Peddle, Bill Seiler, and John
Feagans create a computer in time for the June 1977 Consumer
Electronics Show , and gave them six months to do it. Tramiel's son,
Leonard , helped design the
PETSCII graphic characters and acted as
quality control. The result was the first all-in-one home computer,
the PET, the first model of which was the PET 2001. Its 6502 processor
controlled the screen, keyboard, cassette tape recorders and any
peripherals connected to one of the computer's several expansion
ports. The PET 2001 included either 4 kB (2001-4) or 8 kB (2001-8) of
8-bitRAM , and was essentially a single-board computer with discrete
logic driving a small built-in monochrome monitor with 40×25
character graphics, enclosed in a sheet metal case that reflected
Commodore's background as a manufacturer of office equipment . The
machine also included a built-in Datasette for data storage located on
the front of the case, which left little room for the keyboard. The
data transfer rate to cassette tape was 1500 baud , but the data was
recorded to tape twice for safety, giving an effective rate of 750
baud. The computer's main board carried four expansion ports: extra
memory, a second cassette tape recorder interface, a parallel ("user")
port which could be used for sound output or connection to "user"
projects or non-Commodore devices and a parallel
IEEE-488 port which
allowed for daisy-chaining peripherals such as disk drives and
printers.

The PET 2001 was announced at the Winter CES in January 1977 and the
first 100 units were shipped later that year in October. However, the
PET was back-ordered for months and to ease deliveries, early in 1978
Commodore decided to cancel the 4 kB version (also because the user
would be left with barely 3 kB of RAM).

Commodore was the first company to license Microsoft's 6502 BASIC,
but the license agreement nearly drove Microsoft into receivership as
Commodore stipulated that they would only pay for the BASIC license
after the PET began shipping. However, this took over six months to
finally happen, during which time Microsoft lost money and even worse,
had their cash reserves further depleted by a lawsuit over ownership
of Altair BASIC. At the end of the year, the struggling company was
saved by Apple's decision to license Microsoft BASIC for the Apple II
line.

Although the machine was moderately successful, there were frequent
complaints about the tiny calculator-like keyboard, often referred to
as a "chiclet keyboard " because the keys resembled the chewing gum it
was named after. The key tops also tended to rub off easily.
Reliability was fairly poor, although that was not atypical of many
early microcomputers. Because of the poor keyboard on the PET,
external replacement ones quickly appeared. The PET had somewhat of a
competitive advantage over its
Apple II and
TRS-80 rivals as both were
using relatively primitive integer BASICs for their first six months
on the market while the PET had a full-featured BASIC with floating
point support, a sophisticated screen editor, and lowercase letters,
the last being a feature that the two competing platforms would not
have for a few years. On the other hand, Commodore was a year behind
Apple and Tandy in making disk drives available for their computers.

In 1979, Commodore replaced the original PET 2001 with an improved
model known as the 2001-N (the N was short for "New"). The new machine
used a standard green-phosphor monitor in place of the light blue in
the original 2001. It now had a conventional, full-sized keyboard and
no longer sported the built-in cassette recorder. The kernel ROM was
upgraded to add support for Commodore's newly introduced disk drive
line. It was offered in 8kB, 16kB, or 32kB models as the 2001-N8,
2001-N16, and 2001-N32 (the 8kB models were dropped soon after
introduction). The 2001-N switched to using conventional D
RAM instead
of the 6550 (1kx4) S
RAM in the original model. PET 2001-8Ns had eight
2108 (8kx1) DRAMs and 2001-16Ns used sixteen 2108s. The PET 4016 used
eight 4116 (16kx1) chips. All 32k PETs used sixteen 4116 chips.
Finally, Commodore added a machine-language monitor to the kernel ROM
that could be accessed by jumping to any memory location with a BRK
instruction. It did not include a built-in assembler and required the
user to enter hexadecimal numbers for coding.

Sales of the newer machines were strong, and Commodore then
introduced the models to Europe. The result was the CBM 3000 series
('CBM' standing for Commodore Business Machines), which included the
3008, 3016 and 3032 models. Like the 2001-N-8, the 3008 was quickly
dropped. The change to CBM occurred because of a trademark dispute
with Philips over the PET name.

In 1980, the 4000-series PETs were launched. These used a larger 12"
monitor with a redesigned CRT controller and also included the
enhanced BASIC 4.0, which added commands for disk functions. By this
point, Commodore discovered that people were buying cheaper 8 kB and
16 kB models of the 3000-series and upgrading the
RAM rather than pay
extra for the 32 kB model. Because of this, they punched out the
memory sockets in the 4016 (there was no 8 kB 4000-series PET) to
prevent that practice. The 4032 was a major success in schools, where
its tough all-metal construction and all-in-one design made it better
able to stand up to the rigors of classroom use. Just as important in
this role was the PET's otherwise underutilized
IEEE-488 port. Used
wisely, the port could be used as a simple local area network and
allowed printers and disk drives (which were then very expensive) to
be shared among all of the machines in the classroom.Unlike later
Commodore machines, PETs had no kernel ROM functions for the IEEE-488
port and users had to write their own for using peripherals such as
modems.

The PET's simple, rugged design and completely enclosed components
made it an early favorite in the North American education market. At
one point Commodore owned 67% of the Canadian education market.
Schools preferred the 40-column models because the 40-column display's
larger characters vs. the 80xx PETs were easier for young children to
read. Commodore manufactured a variation on the PET called "Teacher's
PET" - these were relabeled 2001-series PETs which were donated by
Commodore as part of a "buy 2 get 1 free" program offered to schools
as part of a promotion/tax write-off scheme.

Two more machines were released in the PET series. The 8000 series
included a new display chip which drove an 80×25 character screen,
but this resulted in a number of software incompatibilities with
programs designed for the 40 column screen, and it appears to have
been unpopular as a result. The machine shipped with 32 kB standard as
the 8032, but allowed another 64 kB to be added externally. Later the
upgrade was installed from the factory, creating the 8096. Unlike the
40-column models, 8000-series PETs came standard with a 1-channel
speaker for sound generation.

2001/3000 and 4000-series PETs used what became known as the
"graphics keyboard". Numbers were exclusively on the numeric keypad
and the row above the alphabet keys had only punctuation symbols. The
3032 and 4032 were produced in two special variants known as the B
models with the so-called "business keyboard", which had a
conventional layout with mathematical symbols and numbers above the
alphabet keys. The keypad contained only numerals. On the other hand,
all 8000-series PETs sported the business layout.

The 4000/8000 PETs were more explicitly targeted at
professional/business use than the 2001/3000. Business customers were
the main target for the features of the enhanced BASIC 4.0, and a good
selection of prepackaged business software was available. A large
line of 5.25" and 8" floppy drives were made for the PET family, and
even 5 and 7MB external hard disks . While they became fairly popular
for business use in Europe, they failed to make much impact on the US
market in part because the 6502-based PETs could not run
CP/M , which
had become the standard for business software. In addition, the PET's
32k of memory was a disadvantage against the
Apple II and TRS-80, both
of which could accommodate 48k.

As noted above, 4000 and 8000-series PETs used larger monitors and a
different video controller than the 2001/3000 models. This created a
notorious compatibility problem known as the killer poke . On
2001/3000 PETs, there was a register which when enabled did not allow
reading/writing of the video
RAM except during the vertical blanking
in order to prevent snow on the screen (caused by the CPU and video
controller trying to access the V
RAM at the same time). Ordinarily,
this feature was enabled on power-up. If the user didn't mind snow, he
could turn it off and get faster text output. BASIC programs and some
machine-language software commonly did this for performance reasons.
4000/8000 PETs used a video controller based on the
Motorola 6845 CRTC
chip (unlike the TTL logic circuit in 2001/3000s) that eliminated the
snow problem, but also placed a CRT control register in place of where
the VBLANK flag had been on the 2001/3000. Hence software that tried
to disable it would end up throwing the monitor out of sync and
destroying the flyback transformer . BASIC programs intended for the
2001/3000 thus had to be modified in order to run safely on the
4000/8000. Later 40xx/80xx PETs had modified video circuitry to
prevent killer poke damage; a TDA 1170 chip was used in place of the
original analog circuit so that if no sync went to the monitor, it
would merely be shut off rather than sent spurious signals. Video RAM
on the PET used 1kx4 SRAMs. These consisted of two 6550s (original PET
2001), two 2114s (all later 40 column models), or four 2114s (80
column models).

The PET 2001 and 2001-8N had a register that would disable the video
output; this was also used as output for the
IEEE-488 interface, so
screen flicker would occur during disk drive or printer use. It also
became a popular method of producing explosion effects in games,
however the 16 and 32k models removed the screen disable register so
this trick no longer works.

The last in the series was the SP9000, known as the SuperPET or
MicroMainframe. This machine was designed at the University of
Waterloo for teaching programming. In addition to the basic CBM 8000
hardware, the 9000 added a second CPU in the form of the Motorola 6809
, more
RAM and included a number of programming languages including a
BASIC in ROM for the 6502 and a separate ANSI Minimal BASIC
-compatible BASIC for the 6809, along with APL ,
COBOL ,
FORTRAN ,
Pascal and a 6809 assembler on floppies. It also included microEDITOR,
a text editor for use in writing and maintaining programs for any of
the 6809 languages. Also included was a terminal program which allowed
the machine to be used as a "smart terminal" as well, so this single
machine could replace many of the boxes currently in use at the
university. Additionally this machine became a remote development
environment where the user could later upload their creation to a
mainframe after completing development and testing on the SuperPET.

Commodore tried to update the PET line with a new redesign called the
CBM-II series (also known as the B series). These were not as
successful and were ultimately abandoned. However, because the PET
remained popular in Europe, the original PET machines were revived and
the
CBM-II case style was retained. These were known as the SK's (due
to the separated keyboard). They also had a swivel monitor.
Originally, standard 8032 boards were retrofitted into these cases.
Later the SK models got a new mainboard that already included the 64
kB extension directly on the board and were sold as 8296 or, with a
built-in 8250 dual disk drive, as 8296-D. The revived PET line also
included a new pair of floppy drives, the SFD-1001 and 2031 (see below
for more info).

Although not officially a member of the PET series, in 1983 Commodore
packaged C64 motherboards in plastic cases similar to the PET
4000-series in order to create the
Educator 64 . This was an attempt
to retake some of the education market they had largely lost by then
to the
Apple IIe .

GRAPHICS DISPLAY

Play media Dutch newsreel from 1979 in which a PET is shown

In the home computer market the PET line was soon outsold by machines
that supported high-resolution color graphics and sound, mainly the
Apple II (which shipped in June 1977), Atari 400/800 (1979), and, in
particular, Commodore's own bestselling VIC-20 (1980/81). Commodore
released a _High Resolution Graphic_ board for the PET using the
Thomson EF936x graphics chip with a resolution of 512×512 pixels. In
addition, the Apple II,
TRS-80 Model I , and Atari 400 (via 3rd party
expansions)/800 could all be expanded to a maximum of 48 kB of RAM
while the PET was limited to 32 kB.

Without the _High Resolution Graphic_ board, the PET's graphics
capabilities were limited to a character set hardwired in ROM . On
many of the PET range's home computer rivals, the look-up address of
the character graphics could be changed and pointed to
RAM , where new
characters could be defined by a programmer to create custom graphics
shapes. From a programming point of view, this was a relatively simple
method of producing good-looking graphics, which used negligibly more
RAM than a standard character display, and significantly less
RAM than
bitmap graphics. Additionally, BASIC programs often could not achieve
acceptable speed animating bitmap graphics, but since this technique
only involved moving character objects on the screen, BASIC could
achieve acceptable performance, and programs written in assembly
language could be even faster using this pseudo-sprite technique than
using bitmap graphics modes. Many BASIC and assembly language programs
were made this way even on bitmap-capable machines. The PET's lack of
a remappable character set is a major weakness in the machine's
design.

Somewhat offsetting this drawback, the PET's ROM-restricted character
set — an ASCII-1963 deviation known as
PETSCII — was one of the
most varied and flexible of the era. It allowed PET games with
rudimentary graphics to be created, exemplified by clones of video
games such as _
Space Invaders _ and _Lunar Lander _. The PETSCII
character set was even flexible enough to allow for the creation of
simple 3D games such as _Labyrinth_. This flexibility was achieved by
the use of two switchable character sets, allowing the choice of
either mixed-case characters, or uppercase with graphics; either could
also be displayed as a reverse field, negative image. For specialized
applications, alternative character sets could be programmed into an
EPROM inserted in the character set ROM socket. Alternative character
set EPROMs with diacritics and mathematical symbols were available in
the aftermarket. A 2001-8B model with katakana keyboard and character
set was sold in Japan. Commodore Pet Katakana Keyboard

Other than a
PC speaker -class beeper, PETs did not have sound
hardware (except for the 8000 models), but it was possible to rig a
circuit up to the 6522 "user" port that could be used to output square
wave tones to an external amplifier, and some games supported this
feature.

The PET had two empty sockets on the motherboard for adding expansion
ROMs, which could be a total of 8k in size. A predecessor to the
cartridge slots on later Commodore machines, they allowed various
software add-ons such as machine language monitors. In addition, it
was common for commercial programs to include a copy protection ROM
that had to be installed prior to running the application; something
of an inconvenience to users owning multiple applications protected in
this way, as the chips would have to be swapped in order to run their
respective programs.

The original lineup of disk drives for the PET were the dual-unit
2040, 3040, 4040, 8050, and 8250. Later (near the end of the PET's
lifespan), single-unit 2031 and SFD-1001 drives were produced that
used the same case as the 1540/1541, but sported the PET's parallel
interface instead of the VIC-20/C64 IEC interface. The 4040/2031 used
the same 170 kB format as the 1541 and is completely read/write
compatible (although software that performs low-level drive access
will not work). 8050 and 8250 drives had an incompatible 500 kB/1 MB
format, but were popular well into the 1980s as server/BBS storage
devices because of their large capacity.

In addition, Commodore had 8" 8060, 8061, 8062, and 8280 drives which
used MFM encoding instead of the GCR used on their other disk drives
and was mainly intended to allow PET users to read disks written on
IBM mainframes/minicomputers. 5 MB and 7.5 MB hard disks were produced
as well. They have no directory support and are treated by the kernel
ROM as simply a larger floppy disk.

All PET peripherals will work on VIC-20/C64/Plus-4/C128 machines with
a parallel → IEC adapter (reverse IEC → parallel adapters were
also made), and as mentioned above, 8050/8250 drives were sometimes
used on C64s for BBS service because of their large capacity and
faster interface.

An alternative option for adding floppy disk capability to the PET
was the Computhink disk system. Although references to this system
are hard to find today, it was nevertheless popular at the time, as it
was both cheaper and considerably faster than the Commodore system and
available from an earlier date. Unlike the Commodore units, it did not
use the
IEEE-488 interface, but instead required an extra circuit
board to be installed inside the PET, connected to the PET's expansion
connector, which used a
Western Digital floppy controller chip to
provide a standard Shugart interface. The board also held extra RAM
for use as a disk transfer buffer, and ROM containing the disk
operating software. This software was not compatible with Commodore
standards and was somewhat awkward to use. Before using the disk
system it had to be initialised manually by issuing the command
SYS45056. This made available a set of "pseudo-BASIC" commands for
performing disk operations, which bore little or no resemblance to the
standard Commodore commands for the same operations and in addition
had to be prefixed with $, thus breaking the rules of BASIC syntax. It
had a severe limitation in that it was only possible to have one file
open at a time which made many common tasks difficult and slow, though
the direct interface to the motherboard made data transfer
significantly faster than the CBM units using the IEEE bus. The
additional code hooked into the BASIC interpreter could slow the
execution of BASIC programs by 20-30%, and it would break with
programs which used the standard POKE to disable user breaks.
Nevertheless, it was still regarded as a useful system and as a great
improvement over cassette storage.